Not even GNOME itself could ignore the GNOME 3 criticism for much longer. "As part of the planning for the DropOrFixFallbackMode feature, we've decided that we will compile a list of supported gnome-shell extensions. This will be a small list, focused on just bringing back some central 'classic' UX elements: classic alt tab, task bar, min/max buttons, main menu. To ensure that these extensions keep working, we will release them as a tarball, just like any other module."

I was not a big fan of Gnome 3 at the beginning... I'm still not, but since I discovered the extensions, It's quite usable.

And I'm using more than one extension in the top panel without any trouble!!

I must admit that I don't need a lot of stuff up there:
I've my "favorite" links in the top panel, CPU Temp, Net Speed, "Places", and a correct "Personal menu" with "Shutdown" in it.
Also got a nice panel at the bottom, that does exactly what it's meant to. And, "Gnome tweak tools" gave me the "reduce window" button back...

I use this configuration on 4 different computer without any trouble and I got my "productivity" back !